The present invention relates to a liquid circuit comprising a liquid storage vessel, a liquid pump, a device which consumes or utilizes the liquid, a filter element having an unfiltered liquid side and a filtered liquid side, and a controller for returning excess liquid not needed by the consumer device at least partially to the filter element.
German Patent No. DE 197 14 488 discloses a method and a fuel injection system for heating a fuel. In the method of heating fuel, the fuel is compressed by a fuel pump to an injection pressure necessary for injection. A part of the compressed fuel is supplied via a fuel filter to an internal combustion engine, where it is injected by fuel injectors. The fuel which is not injected is depressurized via a valve or a leakage line and at least partially supplied to the fuel pump again. The valve opens as soon as the fuel has a fuel temperature below a minimum temperature.
To carry out this method, the fuel injection system has a fuel supply line which is connected to the fuel tank, and a fuel pump is provided for delivering the fuel from the tank into the fuel line, in which a fuel filter for filtering the fuel is positioned. The fuel line is connected to a fuel injector of an internal combustion engine. A valve, which is connected via a return line to the fuel supply line, is provided on the fuel line. The valve opens as a function of predetermined operating states. For this purpose, the valve is constructed as a thermostat valve, which automatically connects the fuel return line to the fuel supply line when the fuel temperature is below a minimum temperature. The return line is connected to the fuel supply line in such a way that the heated fuel mixes with the cold fuel from the tank, whereby the mixing may occur in a mixing chamber.
However, the fuel injection system includes a large number of lines, connected by valves and thermostats to a central processing unit. In addition, numerous fuel lines must be connected to the components. In this case, during the installation of the fuel injection system on an internal combustion engine, there is a significant outlay for installation and there is also a significant danger that different lines may be confused with one another.